Industrial Process Control Applications :
This is a generic or standard controller for any
type of process. Shown here is a temperature controller.
The STC1000 could be used for Ovens or furnaces,
liquid baths,
heating or environment chambers. It has a single analog input and an
analog or relay output.
Analog inputs could be like 4-20 mA, thermocouple
or RTD. Analog
outputs can be 0-10 V for a thyristor drive, SSR drive output or
potential free contacts of a relay to operate external 3 phase
contacters.
The closed loop control could be On-Off or
Time-Proportional. It was
known as digital temperature indicating controller. Sometimes it would
be used just as a Alarm or in a Trip circuit for protecting a system,
when a uP or uC based PID controller fails.
This is used in the processing of plastics,
rubber, metals and in
chemical plants too. Here is a checklist that was made for helping its
fabrication. You can see the limitations in which we manufactured these
products. An optimum quality was evolved, defined by a user's
affordability of the product.
Also see -
Proportional Temperature Controller
This is a Proportional Controller where the setpoint is derived from a
Thumbwheel switch.
The conversion of Thumb-wheel Digital Data to
Analog mV is similar to R-2R
Weighted Resistor Network. In this case it is a 1-2-4-8
Binary Weighted Resistor Network. It has no Digital Components.
In this controller you can see a sensor open
indication. When the
sensor breaks, the temperature controller may continue to turn on the
actuators or heaters, It may even Oscillate. So when a high impedance
is detected in the sensor input terminals, the output relay is shut off
and a LED is turned on to simplify operator's diagnosis.
Mount the controller a distance away from heaters,
ac-drives and
vibrating parts. Avoid direct sunlight on controller, fix controller in
a sealed control panel. Earth the point where the thermocouple senses
heat. Some heaters leak. The machine has to be earthed.
Anantha Narayan
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